The present invention relates to a method for bending and tempering glass sheets supported on a ring mould, in which method
a cold glass sheet is placed on a ring mould, PA1 the ring mould along with its glass sheet is carried through at least one preheating section into a bending furnace, PA1 the preheated glass sheet is heated in the bending furnace to a bending and tempering temperature, and PA1 the bent glass sheet is carried into a tempering section, wherein chilling air is blown to its opposite surfaces.
The invention relates also to a furnace apparatus for bending and tempering glass sheets, said apparatus comprising a loading and unloading station, a plurality of outline moulds provided with carrier wagons therefor, a separate bending furnace and a separate tempering section provided with nozzles for blowing chilling air to the opposite surfaces of a bent glass sheet.
The invention is particularly suitable for bending relatively simple glass shapes that can be bent by the gravitational use of an outline mould. Many of the automotive side windows and backlights are such relatively simple shapes that can be bent by the application of a method and apparatus of the invention. There is a prior known method for essentially the same purpose, wherein a homothermal glass is dropped onto an outline mould and the glass assumes its proper shape by virtue of the inertial force and and configuration of the outline mould. This prior known method offers benefits such as high capacity and operational reliability but it also involves drawbacks, such as expensive price, a rather long shape replacement time (4-5 h), the marks caused by dropping on the edge areas of a glass, and the high price of tools for each particular glass.
On the other hand, there are prior known single furnaces operating on the outline mould principle, wherein the glass is only heated from above and the glass bends to its shape whose bending or flexural depth is determined by adjusting the heating time. The advantage offered by single furnaces is simplicity and a low price but the notable drawbacks include low capacity, a relatively large minimum thickness (typically 5 mm, sometimes 4 mm), simple bending shapes and only a moderate bending accuracy (as the bending depth is only controlled by means of bending time).
An object of the invention is to provide an improved method and furnace apparatus having a favourable price and a compact size in relation to capacity as well as low mould-related costs, facilitating also the bending of glass sheets of varying thicknesses as well as thin glass sheets.
This object is achieved by the invention on the basis of the characterizing features set forth.
Flexible production and a simple replacement of glass shapes are achieved by the invention especially by arranging the movements and heating of each glass sheet individually according to the thickness and measured temperature of the glass sheet. The key factor in providing this individual passage system is a sufficient length for a bending furnace for facilitating the commencement of the passage of glass sheets in an accelerating motion towards the tempering section and a relatively long accelerating motion in the bending furnace even prior to reaching a final bending shape. When the glass sheet reaches a predetermined tempering temperature, which is higher, the thinner a glass sheet in question, the passage motion is instigated in the furnace, the glass sheet reaching its final shape during the passage and, at the same time, the glass sheet reaches a sufficiently high traveling speed in view of advancing from the furnace into the tempering section in a time as short as possible.
This differs essentially from the prior known furnace assemblies, wherein the passage from the bending furnace to the tempering section is started when the leading edge of a glass sheet is as close to the discharge opening of the bending furnace as possible, so that the deformation between the commencement of passage and the tempering would be as slight as possible.
The glass sheet is supported on the same outline mould throughout the handling process. Loading and unloading are effected at the same station, whereby the glass sheets proceeding from loading to preheating are forced to travel below the tempering section. Preheating sections are located on two levels and, thus, at least one preheating section is located below the bending furnace.